The present invention is directed to an asynchronous interface for use between two electronic musical instruments, each of which employs a digital multiplexed keying scheme. The keying of one instrument is made responsive to the keying information from the other instrument although the two instrument clocks are asynchronous.
In the construction of electronic musical instruments, namely electronic digital organs, it is often desirable to utilize a basic building block approach for creating a varied product line. Aside from the manufacturing advantages of such an approach, there are significant musical advantages as well. The warmth and richness of the string section in a symphony orchestra is due in part to the multiplicity of like instruments, each contributing a uniquely different quality to the total sound. In musical terms this is referred to as ensemble. Ensemble is a very important consideration when building an electronic musical instrument to simulate the sound of a multi-rank pipe organ. A significant contribution to the ensemble quality of an electronic organ has been the use of multiple systems where each system maintains an independence of sound quality.
In completely digital tone generation systems, such as the Allen digital computer organ, each system has its own independent clock and voicing specification along with other qualities important to ensemble. The keying of such a system utilizes digital time division multiplexing, the timing being derived from the system clock. It is not possible to key two or more such systems from a single set of keys by connecting the systems in parallel because the independently clocked systems would interact adversely.
In the past there have been two approaches to the problem of keying such multiple systems. One approach is to have more than one set of key contacts per note so that each independent system has its own set of controls. This method is not only costly to implement but costly insofar as the time required to adjust the many key contacts involved. This approach becomes more impractical as the number of paralleled systems increases.
The second approach to the problem is to use interface devices called keyers. A keyer is an array of electronic switches where each key of the organ is wired to one electronic switch in the array. The output of the array accepts the multiplexing signals from its associated system. Since the key switches operate in a DC mode, any number of keyers may be connected to one set of key contacts. The disadvantage of this method of keying is the significant amount of wiring required i.e., one wire per key per system. This approach is not only costly to implement due to extensive wiring, but costly in terms of the space required to house the many keys required in a large organ system.
It is an object of the present invention to eliminate those disadvantages noted above by providing an asynchronous serial interface between two independently clocked digital organ systems which employ multiplexed keyboard information, where only one system interacts directly with the key switches.